Working Principle of Limit Switches

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The working principle of limit switches mainly triggers the internal contacts through mechanical motion, thereby realizing the on-off of the electrical circuit and further controlling the operating state of mechanical equipment. The specific introduction is as follows:

### Structural Composition
Limit switches are usually composed of operating mechanisms, contact systems, springs, housings and other parts.
- **Operating Mechanism**: It is the part connected to the mechanically moving parts. Common forms include push rods, rollers, levers, etc., which are used to detect the position and motion state of objects.
- **Contact System**: It includes normally open contacts, normally closed contacts, and one or more moving contacts. In the initial state, the moving contact is closed with the normally closed contact and disconnected from the normally open contact.
- **Spring**: It is used to restore the operating mechanism and contacts to their initial positions after the external force disappears.
- **Housing**: It plays a role in protecting the internal structure. Usually, it has a sturdy housing and sometimes has functions such as waterproof and dustproof.

### Working Process
- **Triggering Action**: When the monitored object moves to a specific position, it will directly or through the transmission rod push the operating mechanism. For example, in the direct-acting limit switch, the impact block on the moving part presses the button to make its contacts act; in the roller limit switch, the stop iron of the moving machinery presses on the roller of the limit switch, and the transmission rod rotates together with the rotating shaft, so that the cam pushes the impact block. When the impact block is pressed to a certain position, it will quickly actuate the micro switch; in the micro limit switch, when the push rod is pressed down, the bow spring sheet deforms, stores energy and generates displacement. When the predetermined critical point is reached, the spring sheet together with the moving contact generates an instantaneous jump.
- **On-Off of the Electrical Circuit**: The action of the operating mechanism will cause the moving contacts in the contact system to move, thus changing the closed or open state of the contacts. Under normal circumstances, when the limit switch is not triggered, the normally closed contacts are closed and the electrical circuit is in a conducting state; when the limit switch is triggered, the normally closed contacts are opened and the normally open contacts are closed, and the on-off state of the electrical circuit changes.
- **Reset Process**: When the object is removed, the operating head will automatically return to its initial position under the action of the spring, and the contacts will also be reset accordingly. For example, in the direct-acting limit switch, after the moving part leaves, its contacts will automatically reset under the action of the spring; in the roller limit switch, after the stop iron on the roller is removed, the reset spring will make the limit switch reset.